UCLA

CO2 hydrogenation has been regarded as both a mitigating solution to harmful greenhouse gas emissions and a production method of high-value chemicals and fuels. Due to the thermal stability of CO2, a precursor C1 building block is needed to start the formation of the C2+ products. Significant research has been done on this area and two possible pathways have been identified: the methanol-synthesis route, where the C1 precursor is methanol, and the Fischer-Tropsch synthesis (FTS) route, which utilizes CO as the C1 precursor. For the FTS route, Fe and Co catalysts have proven to be the most promising. However, the wide range of products and the limitation in selectivity towards C2+ olefins impose challenges on understanding and analyzing the underlying mechanisms. This issue is shown to be minimized when alkali metal promoters are incorporated into FTS catalysts. Using experimental evidence of a K-promoted Fe-Co catalyst’s efficient activity towards CO2 hydrogenation and C5+ high selectivity, this work utilizes computational investigations to elucidate the underlying mechanisms. We utilize Density Functional Theory (DFT) to model the catalyst’s active site (Fe-carbide phases), analyze its stability, understand the impact of the Co additive when dispersed within the catalyst, and gain an understanding of the synergetic effect between Co and Fe. Additionally, possible pathways for the formation of C1 intermediate species followed by their C-C coupling to form valuable C2+ products are traced. This comprehensive study on the active iron-carbide surface contributes to establishing a correlation between catalytic efficiency (activity and selectivity), and the synergetic effects of Fe-Co catalysts. Moreover, this correlation will play a crucial role in fine-tuning highly efficient catalytic systems for the production of specific desired C2+ chemicals.